Several studies on these 3 approved CDK4/6i demonstrated that their toxicity profile can be easily managed with supportive care measures, dose reduction, and/or temporary drug interruptions.1-6,13-15 Hematologic side effects, such as neutropenia, anemia, and thrombocytopenia, are the most commonly experienced by patients receiving CDK4/6i-based therapy. This evidence concerns the gene CDK4 and neutropenia.